<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>CSS 3-box</title>
    <style type="text/css">
        .container{height:200px; width:200px; border:1px solid #ccc;}
        div.box{box-sizing:border-box; -moz-box-sizing:border-box; -webkit-box-sizing:border-box; width:50%; border:1rem solid #000; float:right; text-align:center;}
    </style>
</head>
<body>
    <div class="container">
        <div class="box">left</div>
        <div class="box">right</div>
        <div class="box">left</div>
        <div class="box">right</div>
        <div class="box">left</div>
        <div class="box">right</div>
        <div class="box">left</div>
        <div class="box">right</div>
        <div class="box">left</div>
        <div class="box">right</div>
    </div>
</body>
</html>
